Xilio Therapeutics, Inc.

(a)

Departure of Chief Medical Officer

On May 11, 2026, Katarina Luptakova, M.D., notified us of her decision to resign as chief medical officer effective May 31, 2026 to pursue other opportunities. We have engaged Martin Huber, M.D., to serve as a medical and clinical consultant on an interim basis. Dr. Huber most recently served as president and chief executive officer of Mersana Therapeutics, Inc. (prior to its acquisition by Day One Biopharmaceuticals, Inc.), and prior to that served as president and head of R&D at Xilio.

Appointment of Principal Accounting Officer

On May 11, 2026, our board of directors appointed Christopher Frankenfield, our chief operating and financial officer and principal financial officer, to also serve as our principal accounting officer effective as of that date. Upon Mr. Frankenfield’s appointment, our former principal accounting officer ceased to serve in such role.

Christopher Frankenfield, age 44, has served as our chief financial officer since August 2024 and our chief operating officer since August 2023. Mr. Frankenfield previously served as our chief legal and administrative officer from August 2022 to August 2023 and as our general counsel from March 2021 to August 2022. Prior to joining us, Mr. Frankenfield served in roles of increasing responsibility at Blueprint Medicines Corporation, or Blueprint, from August 2015 to March 2021, including as vice president of corporate legal affairs from July 2019 to March 2021. While at Blueprint, Mr. Frankenfield was responsible for a range of corporate legal activities, including public company reporting, capital markets strategy and follow-on equity offerings, collaborations and partnerships, and supporting commercial product launches. Prior to joining Blueprint, Mr. Frankenfield was a senior associate at Wilmer Cutler Pickering Hale and Dorr LLP, where his practice focused on capital markets and strategic transactions, public company reporting and corporate governance matters. Mr. Frankenfield began his career in the advisory practice at PricewaterhouseCoopers LLP. He received his B.A. in economics from the College of William & Mary and his J.D. from the University of Virginia School of Law.

Mr. Frankenfield does not have a family relationship with any of our officers or directors and has no direct or indirect interest in any transaction required to be disclosed pursuant to Item 404(a) of Regulation S-K.

There have been no changes to Mr. Frankenfield’s compensatory plans or arrangements in connection with his appointment described herein.

(c)

Director and Officer Trading Arrangements

None of our directors or officers adopted orterminated a Rule 10b5-1 trading arrangement or anon-Rule 10b5-1 trading arrangement (as such terms are defined in Items 408(a) and 408(c) of Regulation S-K, respectively) during the quarterly period covered by this Quarterly Report on Form 10-Q.